Bill Gates dropped out of Harvard to focus on Microsoft.
By the time he got to Harvard University, Gates had already been programming computers for at least five years. He created a computerized version of tic-tac-toe when he was 13 years old.
Gates dropped out of Harvard in 1975 to focus on Microsoft full time. The move sparked a lifetime of success for Gates, who is now estimated to be the richest man in the world.
Microsoft cofounder Paul Allen ditched Washington State University to join forces with Gates.
While taking classes together in high school, Allen and Gates went into business together for the first time and created Traf-O-Data, a tool for tracking traffic flow in the Seattle area. After high school, they separated when Gates went to Harvard and Allen went to Washington State University, according to Forbes.
The two dropped out of their respective schools to team up once again and start Microsoft.
Oprah Winfrey left Tennessee State University to pursue a career in media.
Winfrey established her love for media while at East Nashville High School. She was on the speech team and worked for a local radio station, and she carried that passion with her to college.
Michael Dell started Dell from his University of Texas dorm room and left to see it through.
Dell enrolled at the University of Texas as a pre-med student, but his love for computers almost immediately took over. As a freshman, Dell used $1,000 to purchase and upgrade old computers and sell them for a profit, Entrepreneur reports.
According to Forbes, Dell was selling around $80,000 a month and decided to drop out at age 19 to pursue the computer business.
Whole Foods founder John Mackey dropped out of college multiple times.
Mackey wasn't able to stick it out in college, and dropped out of several different Texas colleges in the mid '70s. "I was in and out of college for six years," he told CBS. When he was 25, he was a religion and philosophy major at the University of Texas. He joined a vegan co-op, met a girl, dropped out for the final time, and borrowed money to open his first grocery store.
Fast forward several decades and Whole Foods has become an international chain with more than $14 billion in annual sales.
Steve Jobs dropped out of Reed College after a semester.
The late Apple cofounder enrolled in Reed College in Portland, Oregon, in 1972, but his tenure lasted only one semester, according to CNN. After dropping out, Jobs worked as a video game designer for Atari and then backpacked through India.
When he returned, he teamed up with high school friend Steve Wozniak. By 1975, the duo had started to work on the first Apple product in the Jobs family garage. The Apple 1 was released in 1976.
Beanie Babies billionaire Ty Warner left Kalamazoo College to become an actor.
Warner dropped out of Kalamazoo College in Michigan after one year to pursue an acting career in Hollywood, Chicago Magazine reports. It didn't pan out, so Warner got a job with Dakin Toy Company, where his father worked.
Warner was fired in 1980 for selling plush toys of his own, and during a three-year stay in Italy, he discovered plush-toy cats that he'd never seen before. He returned home to make plush animals, and in 1986 he founded Ty Inc., the maker of Beanie Babies. By 1998, the company's annual sales had reached $1.4 billion, and Forbes now pegs Warner's net worth at $2.5 billion.
Elizabeth Holmes dropped out of Stanford to build her company Theranos.
When she was a sophomore at Stanford in 2003, Holmes founded healthcare-technology company Theranos. A few months later, she dropped out to focus on the company.
Matt Mullenweg left the University of Houston to start WordPress.
Mullenweg dropped out of the University of Houston in 2004. Even then, he was so precocious that he didn't bother taking computer classes. At 20, he had already developed the beginnings of WordPress and was fielding job offers from tech companies, the Houston Press reports.
After he dropped out, he went to work for CNET in San Francisco, with a promise that he could continue developing his side project 15% of the time. He left to found Automattic, the company behind WordPress. Despite only employing 330 people, the online platform now has 131 million unique visitors per month and powers 23% of the web.
Mark Zuckerberg dropped out of Harvard to focus on Facebook full time.
Zuckerberg first launched Facebook from his Harvard dorm room. He dropped out in 2004 after his sophomore year and moved to Silicon Valley to work full time on what has become the world's largest social network, with more than 1 billion active users.
Oracle billionaire Larry Ellison dropped out of two colleges.
Ellison began his college career at the University of Illinois at Urbana-Champaign, but he dropped out after two years. After a summer in California, he decided to transfer to the University of Chicago. He dropped out again after one semester and went back to California.
Ellison worked a number of jobs before joining Ampex Corporation, where he was responsible for building a database for the CIA. He nicknamed it "Oracle." In 1977, Ellison and two coworkers created a database management company that is now known as Oracle Corporation.
Enterprise Rent-A-Car founder Jack Taylor dropped out of Washington University to enlist in the Navy.
Taylor was a business student at Washington University in St. Louis when he left school and enlisted to serve as a pilot during World War II. Taylor returned to St. Louis and started Enterprise Holdings, which powers Enterprise Rent-A-Car, with a fleet of seven cars and one employee. He named the company after the aircraft carrier he served on during the war, the USS Enterprise.
Taylor ran the business until 1991, when he passed it down to his son. Forbes estimates he and his family's net worth to be north of $12 billion.
Daniel Ek dropped out of a university in Sweden and later cofounded Spotify.
In 2005, Ek left his studies in engineering at the Royal Institute of Technology in Sweden after eight weeks, according to Forbes. He worked for multiple websites and eventually founded an online marketing company called Advertigo. Ek sold the business to Swedish company TradeDoubler. He later teamed up with its founder to start Spotify in 2008.
Spotify took off, and Ek became a millionaire just a few years later. According to its website, the music streaming service now has more than 75 million active users.
Sophia Amoruso dropped out of community college before starting Nasty Gal.
Amoruso struggled her way through high school and had to be home-schooled to finish. She then became a community college dropout.
But in 2006, Amoruso started an eBay store selling vintage women's clothing. The edgy fashion retailer Nasty Gal is now a multimillion-dollar business. She details its growth in her book "#GIRLBOSS."
JetBlue Airways founder David Neeleman dropped out of the University of Utah a year before graduation.
Neeleman discovered his knack for business when he was a child working at his grandfather's grocery store, but a learning disability often limited his success academically. After three years at the University of Utah, Neeleman dropped out.
He went on to found the commercial airlines Morris Air, JetBlue Airways, and Azul Brazilian Airlines.
Arash Ferdowsi dropped out of MIT and cofounded DropBox.
Ferdowsi dropped out of the Massachusetts Institute of Technology in 2007 after three years at the school, according to Inc. He left to cofound DropBox, which quickly grew from a tiny startup to a service used by hundreds of millions of people.
Ferdowsi is now a millionaire and the company's current chief technology officer.